[Enzymatic determination of sodium, potassium and chloride in plasma]

The Boehringer enzymatic reagents for Na, K and Cl determination on a Hitachi 717 automatic analyser at 37 degrees C were evaluated. Except for Na, the within-run and between-run precision assays gave CV within the SFBC ranges but were higher than those of the comparison analysers: Ektachem 500 Kokak, Dimension Ars Du Pont-De-Nemours and flame photometry. The linear ranges were larger than the usual clinical results. Accuracy, estimated from human controls, was 99 to 103% for Na and K, and 105% for Cl. Comparison of plasma from 102 to 152 patients showed a good concordance for sodium with the Dimension ARS (y = 1x + 0). On the contrary, with Ektachem Kodak, differences appeared, particularly for high values (y = 0.91x + 13.6). For potassium, the concordance was good with flame photometry (y = 1x + 0.1) and Ektachem Kodak (y = 0.94x - 0.16). For chloride, comparison was satisfactory except for high values which were underestimated by the enzymatic method: Dimension ARS (y = 1.03x - 4.8), Ektachem Kodak (y = 0.91x + 9.8). The enzymatic methods were very easy to perform and can be adapted on any autoanalyser at 37 degrees C. We conclude that they are suitable for routine clinical determination. Urinary assays are currently being developed.